I have same issue with Slaves and Masters quest.
I have first encountered a Spider Queen, so i killed it. Then i encountered Frederick. Gave him the bloodstone right at that moment when i find him. He sayed something like i corrupted star stone and i should die, and run to the entrance into the madino cave. So i entered that cave, explored it. Found Frederick in it. He was sitting again with his leg and crying ( like i wasnt giving him a bloodstone, while i already used one on him). I have crafted a Filter of Fearless imp. But cant do anything with it. When i talk to imp there no dialog options about giving elixir, and i cant talk to frederick at all, he just sitting on floor and crying that he is in pain.
So this quest obviously bugged :(((
